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I have a 351W with a Ford 1G 15 volt 55 amp #D20F-10300-EB alternator. I'm looking to upgrade it to 100+ amps. I could go to a 3G, but I don't know whether I would need to change mounting brackets, and I'd like to avoid that.

In researching 1G units, there are 2 models, 7074 and 7078. What's the difference, and is it important for my application?

Also this alternator parts house has a 130A upgrade kit for a 1G. Would this be a good alternative to buying a new one from Summit or Jegs?

More background if needed: The 351W is a replacement engine put into a 69 Mustang. I think the engine came from a late 80-early 90s F-150 (someone else did the swap before I got it, so I don't have a specific year). The present alternator works, but the voltage drops enough when I'm running lights, wipers, turn signal, radio, then step on the brakes -- the radio shuts down for low voltage. Thankfully, the car keeps running, but I definitely need more amperage.

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Honestly, I don't think you need an upgraded alternator. I suspect you need a new or rebuilt alternator of the same output.

It's not an ambulance, or a plow, or a winch truck. Your current alternator (if in good shape) should be able to keep up with a 40-50 amp load, which I'm guestimating is your "worse-case" load you described.

Before trying to upgrade, have your current alternator checked out. If it checks out okay and you still feel you need more, consider a smaller pulley - a bunch cheaper than an upgrade.

Beyond that I'm not knowledgeable about these specific FoMoCo alts to know if there's a "drop-in" replacement that will yield more amps.

However, as I said - I don't think you need it. UNLESS your "stereo" is of the competition variety that dims lights in neighboring towns and cannot actually be listened to inside the vehicle without hearing loss...

I'm sorry, what??

ON EDIT:

Oh, and make darn sure your battery cables and "D+" lead are not corroded and have clean connections. On a '69 with a donor engine (especially Ford) I'll bet that four-to-five decade old D+ lead is all green copper inside. Your charging loss might very well be in the wires alone. Perform a "voltage drop" test across the B+, D+, and battery ground cables.

I'm a huge Bronco fan and this has always been a problem. Easily solved.

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  • I do have a small (10") subwoofer which will draw a little amperage, too. Great thought about the wiring, especially the alternator-to-battery. It's probably too small!
    – Bill N
    Nov 11 '17 at 15:28
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As far as I can tell the 7074 number refers to the higher amp 1g alternators (90+A). While the 7078 seems to refer to the lower amp alternators. Then there are variations on the number which seem to refer to the number of grooves on the pulley as well as clock position.

According to http://www.mustangandfords.com/how-to/interior-electrical/1407-how-to-identify-and-select-ford-alternators/ the 1g, 2g and 3g alternators are interchangeable. You would have to take the voltage regulator wiring into consideration if you did swap 1g (internal or external) to 3g (internal). The site also mentions that there are many variations to the Ford 1g alternator cases.

Although purists and restorers have spent a lot of time trying to sort out 1G alternator case differences, there are no pat answers. Some have Autolite on them, while some don’t. Some have the teardrop at the rear of the case, while others don’t. There are aftermarket 1G cases as well adding to the confusion. Ideally, you will find a complete 1G core or castings appropriate for your restoration.

IMO since you have an alternator case that fits, your best option (if you want a higher amp alternator) would be to go with the upgrade kit and have a professional rebuild it.

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  • Thanks! I did see that site about "how to identify" but I didn't see anything about 7074 vs 7078. I'm not really looking for a concours restoration, just want to avoid retooling all the mounting brackets. If upgrading the wiring harness doesn't work (see SteveRacer answer), I'll probably just get a Summit Racing 100 amp.
    – Bill N
    Nov 11 '17 at 15:28

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